1. Field of the Invention
The present invention relates generally to a multi-disk friction clutch. More particularly, the present invention relates to a multi-disk friction clutch having means for promoting uniform engagement and wear of the friction disks.
2. Description of the Related Art
Friction clutches for use in transmitting rotational torque between a motor vehicle engine and a transmission are well known in the art. One known friction clutch design includes two friction disks, a pressure plate, an intermediate plate, and a clutch cover mounted for rotation about a common axis. The clutch disks, pressure plate and intermediate plate are axially moveable relative to each other so that the pressure plate may be moved relative to the cover to press the two friction disks and the interposed intermediate plate axially against an engine flywheel. A series of drive straps, each generally including one or more resilient elements that are layered to form a leaf spring, are placed around the peripheries of the intermediate plate and pressure plate to provide a biasing force against the plates. During engagement of the clutch, the intermediate plate, pressure plate and friction disks are pressed against the engine flywheel, such that rotation of the flywheel causes rotation of the friction disks. During disengagement of the clutch, the drive straps bias the intermediate plate and pressure plate in a direction away from the flywheel to separate the intermediate plate and pressure plate from the friction disks.
A basic problem with conventional friction clutches is that the intermediate plate is uncontrolled during engagement and disengagement of the clutch. In other words, it is generally difficult to achieve simultaneous engagement of the intermediate plate and the pressure plate with the friction disks and simultaneous disengagement of the friction disks from the interposed intermediate plate. If the friction disks are engaged sequentially rather than simultaneously, the friction material on one friction disk may be consumed more rapidly than the friction material on the other friction disk, thereby reducing the useful life of the clutch.
To ensure virtually simultaneous engagement of the friction disks, several designs have been proposed that force the travel of the intermediate plate to closely coincide with pressure plate travel. One known design incorporates a mechanism that includes a separator element bolted to the radially outer side of the intermediate plate and a lever attached to the mid-point of the drive straps that bias the pressure plate. Engagement of the separator element with the lever limits axial movement of the intermediate plate to approximately half of the axial movement of the pressure plate during engagement and disengagement of the clutch. Accordingly, the friction disks are engaged by the intermediate plate and pressure plate nearly simultaneous, providing substantially uniform wear of the friction disks and a smooth engagement of the clutch.
One limitation of the aforementioned design is that it requires a hole and/or slot to be machined into the radially outer surface of the intermediate plate to connect the mechanism. Another limitation is that the mechanism must be affixed to the intermediate plate using a separate fastener(s), which, together with the machined holes and/or slot in the intermediate plate, add to the complexity and cost of manufacturing the prior art clutch assembly. Still another limitation is that the separator element must directly engage the lever to protect the drive straps from direct and damaging engagement by the separator element, and to provide a more precise control of the displacement of the pressure plate relative to the intermediate plate. Yet another limitation is that maximum axial movement of the intermediate plate is generally uncontrolled, permitting the connected drive straps to be overextended and damaged.
Accordingly, there exists a need for a simplified device that can be easily and cost effectively affixed to a clutch to achieve the desired control of intermediate plate travel relative to the pressure plate.